In semiconductor manufacturing technology, it is generally desired that the critical dimension (CD) of various patterns and features exposed on a substrate be relatively uniform across the substrate. CD uniformity may be attributed to a number of factors. One factor is the flatness of the wafer which affects CD uniformity from one field to another field. Another factor is the difference in etch rates between different areas of the wafer.
Typically, a photoresist is deposited and patterned on a substrate, the patterns being limited to the CD. The patterned photoresist can be reworked if the CD of the substrate is not uniform. For example, if CD non-uniformity of a patterned wafer is found during a post-etching inspection (PEI), additional exposure dosage may be applied to rectify the uniformity.
One way of determining CD is by examining CD sensitivity of the substrate. Currently, an average CD sensitivity is used to determine any additional exposure dosage required. The average CD sensitivity represents the average of all CD sensitivities of all local areas on the substrate. However, the CD sensitivity of one area on the substrate may be very different from another area. For example, the CD sensitivity around the edge of a wafer may be different from the CD sensitivity in the center of the wafer.
Therefore, a need exists for a method and a system that take into consideration any differences in local CD sensitivities when determining an exposure dosage.